In a filter apparatus which purifies the polluted solution such as metal treating solution or the like, when the filter operation is continued, the filter member attached to the filter surface becomes clogged, which causes the inner pressure of the filter apparatus to increase, thereby lowering the efficiency of the filtration.
Then, when the filter member is exchanged or reused, these members must be washed. Although this washing operation is generally carried out by removing the filter member from the filter apparatus, such treatment is troublesome, particularly in removing the filter member from the filter apparatus and is not efficient.
Upon this, there is a method which washes the member automatically as it attaches to the filter apparatus as it is.
In the conventional method of this kind, the once purified liquid with said filter member is washed by the countercurrent of said purified liquid with a pump or the like, or by blowing air from the reversal direction.
However, since the former method is small in amount of flow per unit hour, an expected treatment of the reversal washing cannot be carried out even if the reversal washing is performed for a long period. Accordingly, in order to perform a fixed washing, the use of a large amount of purified liquid, a long driving time and the use of a large capacity of pump are necessary. This causes the defect of increasing the cost of apparatuses.
The latter necessitates to perform the washing after removing the pure liquid at the outlet side of the filter member. Accordingly, it lacks the quickness and necessitates a large air pressure. In addition, this has such a defect that the construction of the filter apparatus becomes complicated. Either of the methods cannot be said to be efficient.
Further, the conventional filter body used for filtration is one which disposes in tension a filter member such as cloth, paper or the like around a cylinder frame. For this reason, it takes much time to exchange said filter member because attaching it in a tightening state is very troublesome. Furthermore, in order to enable the winding operation thereof, the filter member is requested to be a soft material. Accordingly, it is difficult to apply a hard material such as a filter plate made of ceramic or the like.